1. Field of the Invention
This invention relates to a novel apparatus and method for the preparation and supply of a polymerization inhibitor. More particularly, the invention relates to a novel apparatus and method for the preparation and supply of a polymerization inhibitor, which comprises preparing a polymerization inhibitor solution by adjusting a polymerization inhibitor to an appropriate concentration with a concentration-adjusting liquid in a chemical plant handling an easily polymerizable compound, such as (meth)acrylic acid and (meth)acrylic acid ester, and continuing stable supply of the solution to an adequate step (device or path) of the chemical plant. The invention further relates to an apparatus and method for the preparation and supply of a polymerization inhibitor with a view to ensuring stable and safe preparation and supply of a polymerization inhibitor, preventing the chemical plant from inducing polymerization, and precluding the chemical plant from being clogged with a polymer. Especially, the invention relates to an apparatus and method for the preparation and supply of a polymerization inhibitor with the object of transforming a powdery polymerization inhibitor allowing neither easy handling nor easy adjustment of concentration into a solution containing the polymerization inhibitor at an adjusted concentration and adjusting the solution in advance so as to ensure effective manifestation of the effect of preventing polymerization.
2. Description of Related Art
The apparatus, which is now generally used for preparing and supplying a polymerization inhibitor batch-wise, is illustrated in FIG. 1.
The apparatus generally used for the preparation and supply of a polymerization inhibitor, as illustrated in FIG. 1, has a polymerization inhibitor preparing and supplying tank 151 which is provided with a propeller type stirrer 102 adapted to be driven by a motor (denoted by M in the diagram). A polymerization inhibitor input port 155 and a concentration-adjusting liquid input port 159 are disposed above the tank 151, and a polymerization inhibitor solution feed opening 163 is disposed below the tank 151. The polymerization inhibitor input port 155 is connected to a hopper 101 storing a polymerization inhibitor with a pipeline 153. The concentration-adjusting liquid input port 159 is connected to the interior of a chemical plant requiring to use an apparatus for the preparation and supply of such a polymerization inhibitor (as requiring to handle an easily polymerizable compound, for example) (hereinafter occasionally referred to simply as “chemical plant”) or to a concentration-adjusting liquid tank disposed as part of the apparatus for the preparation and supply of the polymerization inhibitor (in the present specification occasionally referred to simply as “concentration-adjusting liquid tank”) with a pipeline 157. The polymerization inhibitor solution feed opening (outlet) 163 is connected to a device or a path at an adequate step in a chemical plant requiring to use the apparatus for the preparation and supply of the polymerization initiator (in the present specification, occasionally referred to simply as “next step”; not shown in the diagram) with a pipeline 161. In the tank 151 mentioned above, a liquid level detector 117 is installed. A valve 107 is disposed on the path of the pipeline 153, a flow rate detector 109 and an on-off valve 108 are disposed on the path of the pipeline 157, and a pump 103, a flow rate detector 165, and a valve 166 are disposed on the path of the pipeline 161. Further, a control device 150 is installed as a control part intended to control the operating parts such as on-off valves in accordance with the outputs from detecting parts such as the liquid level detector and the flow rate detector. In the diagram, the control circuits are indicated with a broken line and the pipelines are indicated with a solid line.
FIG. 6 is a graph showing the time-course changes of the liquid level, the feed quantity of a polymerization inhibitor solution, and the concentration of the polymerization inhibitor in the tank which occur in the operation of the method for the preparation and supply by the use of the apparatus for the preparation and supply of a polymerization inhibitor illustrated in FIG. 1 and depicting in outline the on-off operations of the valves 107 and 108. The method for preparation and supply by the use of the apparatus for the preparation and supply of a polymerization inhibitor illustrated in FIG. 1 will be described below with reference to FIG. 6. The target product concentration of polymerization inhibitor SEQ (sequence control by the use of the control device 150) is started after the hopper 101 has been stored as required with the polymerization inhibitor. The concentration-adjusting liquid valve 108 is opened after the liquid level in the tank 151 indicated by the output from the liquid level detector has reached a region below the level for starting the adjustment (not lower than the liquid level for preventing the occurrence of a pump cavitation=5-20% of the whole volume; the liquid level of {circle around (1)} in FIG. 6). The concentration-adjusting liquid is supplied from the concentration-adjusting liquid tank through the pipeline 157 and the concentration-adjusting liquid input port 159 into the tank 151 till an amount necessary for the preparation (target value; the liquid level of {circle around (2)} in FIG. 6). This supply completes the target product concentration of polymerization inhibitor SEQ (resulting in the closure of the concentration-adjusting liquid valve 108). Then, the valve 107 is opened to start the supply of the polymerization inhibitor from the hopper 101 through the pipeline 153 and the polymerization inhibitor input port 155 to the tank 151 (the part of the operation from {circle around (3)} to {circle around (4)} in FIG. 6). Then, the operation of the stirrer 102 initiated by the instruction from the control device 150 is continued for about 10 minutes to complete the preparation of the polymerization initiator (the part of the operation from {circle around (4)} to {circle around (5)} in FIG. 6). The polymerization inhibitor-containing liquid produced in the tank 151 (in the present specification, occasionally referred to simply as “polymerization inhibitor solution”) is continuously supplied to the next step through the polymerization inhibitor solution feed opening (outlet) 163 and further through the pipeline 161, with the flow rate of the liquid adjusted meanwhile at a substantially constant level as by means of the liquid transfer pump 103 on the pipeline 161 (refer to the graph of FIG. 6 showing the feed rate of the polymerization inhibitor solution).
By this method of preparation and supply, however, it has never been made possible to fix the polymerization inhibitor concentration in the tank during the supply of the concentration-adjusting liquid (the period between {circle around (1)} and {circle around (2)} in FIG. 6) (refer to the graph of FIG. 6 showing the polymerization inhibitor concentration in the tank). Thus, during the adjustment made for raising again the lowered liquid level by the addition of a polymerization inhibitor and a polymerization inhibitor adjusting liquid, the change in pressure attendant on the change in the liquid level or the like induces a variation in the feed rate to the next step or a variation in the liquid temperature. As a result, this method has been at a disadvantage in bringing only an insufficient effect in preventing the polymerization at the next step, by-producing a polymer, inducing the devices and the pipelines to sustain clogging, and degrading the quality of the product (refer to the graph of FIG. 6 showing the feed rate of a concentration-adjusting liquid). Also during the aforementioned adjustment by the addition of a polymerization inhibitor and a polymerization inhibitor adjusting liquid, the short-path of the concentration-adjusting liquid in the tank destabilizes the polymerization inhibitor concentration. The term “short-path” as used herein refers to the creation in the tank of a path through which the concentration-adjusting liquid reaches the polymerization inhibitor solution feed opening without being stirred in the tank together with the polymerization inhibitor. The method under discussion, therefore, is further at a disadvantage in manifesting no sufficient effect in preventing polymerization at the next step, suffering the devices and the pipelines (inclusive of the pipelines extending from the tank to the next step) to by-produce a polymer, inducing this polymer to adhere to and even occlude the devices, etc. and degrading the quality of a product. The plant operation, therefore, must be frequently suspended for the purpose of purging the devices, etc. of the defiling polymer. This frequent suspension is at a disadvantage in demanding tremendous time and labor, consequently degrading the operational efficiency of the preparation aimed at, and defying the object of weight preparation.